1. Technical Field
This invention relates to a method and apparatus for mounting friction elements in disc brakes. A particular embodiment of the invention relates to the mounting of friction elements in a disc brake of the kind in which at least one brake disc is axially slideable with respect to its associated rotatable mounting and the friction elements which frictionally engage braking surfaces at opposite sides of the disc are slideably mounted on a fixed caliper or bridge structure which resists movement of the friction elements under the action of the frictional forces generated by engagement of same with the rotating brake disc during actuation of the brake. Certain aspects of the invention may find wider application than strictly in relation to a disc brake of the kind just enumerated.
2. Related Art
There is disclosed in WO 98/26192 and WO 98/25804 a disc brake of the kind described above in which resilient means is provided in relation to at least one axially slideable brake disc and in relation to at least one axially slideable friction element. The resilient means for the disc provides, inter alia, an anti-tilt mounting function. The resilient means for the friction element serves merely to prevent rattle.
In our above-identified prior published WO specifications, the arrangement adopted in relation to the friction elements for mounting the resilient means with respect to the fixed caliper or bridge structure has been on the basis of using the fixed and stable structure of the caliper or bridge as a mounting for providing the basis or foundation from which the resilient means takes its mounting for exerting the necessary forces on the friction elements. Such an arrangement has been considered a logical basis for the construction of an assembly in which there is a need for a high degree of structural and operational integrity achievable on the basis of, inter alia, simplicity of structure and assembly, and minimization of mechanical wear in use, and related factors.
In the embodiments of these prior proposals there has been adopted the use of a leaf-type spring acting from the caliper or bridge, and mounted thereon by means of fasteners, and a suitable connection to the friction elements accordingly.
One aspect of the construction of springing systems for the friction elements of spot-type disc brakes employing one or more axially floating discs, concerns the matching of the spring effect to the physical characteristics of the friction element concerned, notably the question of whether or not the friction element is double-sided (as occurs in the case of the central friction element between a pair of floating brake discs in a double-disc brake of this kind). There may be other circumstances in which it is desirable to vary the spring force applied to the friction element as between one such friction element between a pair of floating brake discs, the actual construction of the friction element (which affects its mass and inertia) differs from that of its associated single-sided friction elements on the outer side of each of the two brake discs. Likewise, it will be understood, that in addition to the static factors affecting such a friction element, so too the dynamic factors affecting it differ from those of its single-sided neighbors in that the double-sided frictional effects during actuation of the brake differ very substantially (from the single-sided effect) and lead to a requirement, we have discovered, for a differential springing effect as between the two types of friction elements accordingly.
While design or dynamic factors arising in a disc brake of the relevant kind may produce a requirement for a differential springing effect even in relation to a brake having a single sliding disc, as disclosed below and as is likely to be the case commercially, the more usual brake structure comprises at least two discs with a double-sided friction element slidingly mounted between the discs, and which is subjected to significantly different forces from those applied to its single-sided neighbor (on the piston-and-cylinder actuator side of the brake), and these differences lead to a requirement for the above-discussed differential springing effect.
Further related factors which have influenced the basis for the technical advance incorporated in the embodiments of the invention include the fact that our prior unpublished work in this field on the control of friction elements includes (as mentioned above) the use of leaf springs mounted on the fixed caliper of the disc brake and acting on all friction elements in an endeavor to provide the necessary spring effect in a simple structure. Such an arrangement can indeed be constructed to provide the required spring effect. However, improvements in several respects would be potentially capable of providing significant performance advantages in relation to such aspects as simplicity and cost of construction of the resilient means, simplicity of mounting (and the avoidance of the use of fasteners such as cap screws), avoidance of the entrapment of dirt and water, and the reduction of space requirements, with the related potential benefit in relation to vehicle turning circle as affected by the volume of movement described by the brake structure in vehicle turning movements (in relation to steered wheels). A further factor relates to ability to apply the spring effect at the location on the friction element where such is of best effect and preferably in a symmetrical manner, for example at both lateral sides of the friction element where it is mounted on guides for sliding movement towards and away from (at least in terms of relative movement) the associated disc friction surfaces.
The resilient means adopted in the embodiments of the present invention have a resilient effect and generate a corresponding spring force which is of a magnitude such that it is significantly greater than that which is required merely for elimination of rattle, and a distinction is therefore to be drawn between the resilient means of the embodiments of the present invention and previously proposed anti-rattle springs in brakes of various kinds. The spring forces generated in the embodiments of the present invention are at a level such that the friction elements are constrained (by the predetermined spring forces) from sliding on their guides, whereby not only is rattling or noise suppression achieved but also the friction elements are restrained from free sliding movement into contact with the brake discs in an uncontrolled manner.
In described embodiments of the invention, resilient means is provided by the two or more friction elements which are slideably mounted in a disc brake and the resilient means acts on both such friction elements so as to produce a differential resilient effect as between the two friction elements, whereby the resilient effect can be matched to the physical characteristics, including mountings, of the friction elements themselves.
In the described embodiments, the resilient means is adopted in a wire spring format which enables several significant advantages to be achieved, including simplicity of mounting (by means of cooperation between the wire of the spring and suitable drillings or bores or notches in the friction elements). Moreover the wire spring form conveniently enables the springs to incorporate various chosen profiles achieved by bending, whereby the location and geometry of the spring and its connection to the friction elements enables the required differential effect to be achieved. For example one simple way of effecting this is to arrange matters so that the moment of the forces exerted by the spring in relation to the friction element is varied in accordance with the required spring effect either by choosing the length of the moment arm accordingly and/or connecting the spring to the friction element appropriately.
Another aspect of the resilient means in the embodiment, which leads to practical advantages in relation to the general construction of the wire spring which provides the required resilient properties, is that a one-piece construction can be adopted which has a generally channel-shape profile as seen in its operating attitude in plan view and thus the wire spring is able to straddle the opposite sides of the caliper or bridge structure which supports the friction elements in their sliding movement. It will be understood that the adoption of a single wire spring construction enables the differing spring forces required by the friction elements to be applied at opposite ends of each of these. Moreover the spring construction has the inherent simplicity of a wire spring, and is coupled with the easy mounting of same as discussed above. Also the spring has the ability to extend between the spaced friction elements for actuation of each and the wire construction has an inherent tendency not to provide structures offering a trap for foreign matter and debris. In this way there has been provided a spring system for friction element mounting in brakes of the relevant kind which offers significant technical advances.
In the embodiments of the present invention the disc brake incorporates resilient means both in relation to the mounting of the brake discs on their mounting hub and in relation to the brake friction elements or pads in relation to their fixed mounting or caliper.
The resilient means are of a structure and strength chosen to be capable of, both in the case of the brake disc and in the case of the brake friction elements, maintaining these components of the brake assembly in their required working attitudes with respect to the structures on which they are mounted. In other words, the springs or resilient means for the brake discs are constructed so as to hold the brake discs in non-tilted working attitudes as they rotate. Likewise, the resilient means for the friction elements or pads maintain these latter structures in their required attitudes with respect to their fixed mounting or caliper. In both cases, the resilient nature of the resilient means permits under the dynamic conditions arising during use of the vehicle and due to engine vibration and vehicle motion/road surface induced vibration and similar factors, a degree of movement from the defined working position (as opposed to the linear axial sliding movement needed to effect friction element-to-disc engagement and disengagement when commencing and terminating braking) which is needed under normal conditions of vehicle use.
In this regard, it is to be noted that the resilient means or springs used in the embodiments in relation to the friction elements for maintaining same in their normal non-tilted attitudes, differ significantly from the springs disclosed in the above-identified WO 98/25804 and WO 98/26192 specifications in which the pad springs are mere anti-rattle springs not adapted to hold the brake pads against tilting movement, but merely to avoid rattling. Moreover, in the embodiments of the present invention the springs for the discs and for the pads are balanced in terms of their relative loading applied to the discs and the pads in order to achieve the necessary separation of same when braking is discontinued and yet holding the pads and discs against tilting during use. Thus, the spring forces exerted on the pads or friction elements of the present invention are much stronger than those merely to prevent rattling or noise suppression. The spring forces are sufficient to restrain the slideable brake pads or friction elements from moving into contact with the brake discs in an uncontrolled manner. The use of the substantially stronger pad springs in the present embodiment assists in positioning the outer rims of the brake discs in their brake-off position for reducing residual brake torque.